As shown in FIG. 1, a cellular radio communication system is mainly composed of a terminal, a base station and a core network. A network consisting of the base stations is known as a Radio Access Network (RAN), which is in charge of access stratum affairs, such as radio resource management. According to actual conditions, there may be a physical or logic connection between base stations. As shown in FIG. 1, there is a connection between base station 1 and base station 2 or between base station 1 and base station 3. Each base station may be connected with one or more Core Network (CN) nodes. The core network is in charge of non-access stratum affairs, such as is location update etc., and is an anchor point of a user interface. The terminal (or User Equipment, UE) refers to any device that can communicate with a cellular radio communication network, such as a mobile phone or a notebook.
A random access procedure is described in detail in a Long Term Evolution (LTE). A random access procedure of a physical layer mainly includes the transmission of a physical random access preamble and the receiving of a random access response. A Physical Random Access Channel (PRACH) is used for transmitting the physical random access preamble. Before sending the physical random access preamble, a terminal selects a PRACH resource. The PRACH resource herein is an uplink channel time-frequency domain radio resource, which occupies 6 RBs (radio block) in a frequency domain and 1-3 subframes in a time domain, and the duration occupied in the time domain is related to the format of the physical random access preamble sent by the terminal. The terminal selects a PRACH resource by selecting the positions of the first subframe of a PRACH resource in the time domain and the frequency domain. Two key configuration parameters related to this selection procedure consist of a PRACH configuration index and a PRACH mask index. The terminal can receive the PRACH configuration index via a system message or handover signaling, and the PRACH configuration index corresponds to the combination of a set of configuration parameters and indicates the following content: PRACH format, PRACH density (the number of the PRACHs configured in each radio frame), and the time domain position (in Frequency Division Duplexing (FDD), the index directly corresponds to the starting subframe number in the time domain of the PRACH) for the transmission of each PRACH, or the version number (in time division duplexing (TDD), the index indicates the version numbers of several different mapping modes in the time domain) of time domain configuration. For an LTE FDD system, at most one PRACH is configured in the frequency domain, at most 10 PRACHs may be contained in a radio frame, and the PRACHs are all separated in the time domain. All the PRACHs in the frequency domain are identical and are uniformly configured by the base station. For an LTE TDD system, at most 6 PRACHs may be contained in each radio frame, and the PRACHs are mapped first in the time domain and then in the frequency domain; when the time domain resource is not enough for bearing the configured PRACH density through a time domain multiplexing on the premise that the PRACHs are not overlapped in the time domain, multiple PRACHs are multiplexed in the frequency domain, and physical random access configuration tables of FDD and TDD systems are respectively given in the following Tables 1 and 2.
TABLE 1physical random access configuration of an LTE FDD systemPRACHSystemConfigurationPreambleframeSubframeIndexFormatnumbernumber00Even110Even420Even730Any140Any450Any760Any1, 670Any2, 780Any3, 890Any1, 4, 7100Any2, 5, 8110Any3, 6, 9120Any0, 2, 4, 6, 8130Any1, 3, 5, 7, 9140Any0, 1, 2, 3,4, 5, 6, 7,8, 9150Even9161Even1171Even4181Even7191Any1201Any4211Any7221Any1, 6231Any2, 7241Any3, 8251Any1, 4, 7261Any2, 5, 8271Any3, 6, 9281Any0, 2, 4, 6, 8291Any1, 3, 5, 7, 930N/AN/AN/A311Even9322Even1332Even4342Even7352Any1362Any4372Any7382Any1, 6392Any2, 7402Any3, 8412Any1, 4, 7422Any2, 5, 8432Any3, 6, 9442Any0, 2, 4, 6, 8452Any1, 3, 5, 7, 946N/AN/AN/A472Even9483Even1493Even4503Even7513Any1523Any4533Any7543Any1, 6553Any2, 7563Any3, 8573Any1, 4, 7583Any2, 5, 8593Any3, 6, 960N/AN/AN/A61N/AN/AN/A62N/AN/AN/A633Even9
TABLE 2physical random access configuration of an LTE TDD systemPRACHDensityConfigurationPreamblePer 10 msVersionIndexFormat(DRA)(rRA)000.50100.51200.523010401150126020702180229030100311103212040130411404215050160511705218060190612010.502110.512210.52231102411125120261302714028150291603020.503120.513220.52332103421135220362303724038250392604030.504130.514230.5243310443114532046330473404840.504940.515040.5251410524115342054430554405645057460
Providing that a configuration index is given and the subframes for transmitting PRACH are known, the UE indicates the available PRACH resource in one radio frame on the configuration index by using the PRACH mask index. In the case of a random access based on competition, the UE can automatically set the mask index to be 0, which means the UE is allowed to select all random access resources on the PRACH configuration index configured by the current cell; and in the case of a random access based on non-competition, the base station can designate a mask index. The examples of a mask index indicating a PRACH resource in an FDD system and a TDD system are given in Tables 3 and 5, wherein the PRACH index in the tables represents the relative sequence number of the first subframe on a random access resource in one radio frame. For the FDD, the PRACH index is determined according to the ascending sequence of the subframe numbers; and for the TDD, the PRACH index is determined according to the time domain firstly and then the frequency domain.
TABLE 3a diagram of the corresponding relationship betweena PRACH resource index and a subframe in an FDD(PRACH configuration index = 10)PRACH Mask IndexAllowed PRACHSubframe0all2, 5, 81PRACH index 022PRACH index 153PRACH index 28
For the TDD, an uplink subframe and a downlink subframe exist simultaneously in one radio frame, while the PRACH resource exists only in the uplink subframe, thus, Uplink/Downlink (UL/DL) configurations of the radio frame must be taken into consideration. In Table 4, a terminal can obtain the uplink/downlink configurations of the radio frame via a system message or handover signaling. Additionally, the PRACH resource (having the frequency domain distribution as shown in FIG. 2) is identified by a quaternion (fRA,tRA0,tRA1,tRA2), where fRA represents the position of a frequency domain and is valued in the range of [0, 1, 2, 3, 4, 5], tRA0 represents that the distribution of a time domain is in an odd subframe (tRA0=2), or an even subframe (tRA0=1), or both an odd subframe and an even subframe (tRA0=0); tRA1 represents that the time domain position of the PRACH of one frame is in the first half-frame (tRA1=0), or the last half-frame (tRA1=1); and tRA2 represents the offset position of a subframe in a half-frame with respect to the first uplink subframe and is valued in relation to the uplink/downlink configurations, and the PRACH is located in a Uplink Pilot Time Slot (UpPTS) if (tRA2=*).
TABLE 4TDD uplink/downlink configurationsDownlink-to-UplinkUplink-Switch-downlinkpointSubframe numberconfigurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
TABLE 5TDD mask index table(UL/DL configuration 3 and PRACH configuration index = 18)PRACHMaskIndexAllowed PRACHPRACH Resource0All(0, 0, 0, 0), (0, 0, 0, 1), (0, 0, 0, 2),(1, 0, 0, 0), (1, 0, 0, 1), (1, 0, 0, 2),1PRACH Resource Index 0(0, 0, 0, 0)2PRACH Resource Index 1(0, 0, 0, 1)3PRACH Resource Index 2(0, 0, 0, 2)4PRACH Resource Index 3(1, 0, 0, 0)5PRACH Resource Index 4(1, 0, 0, 1)6PRACH Resource Index 5(1, 0, 0, 2)
The designation of the mask index by a network mainly includes two cases: in one case of a handover procedure, the time for initiating a random access in a target cell is determined by various factors after the terminal receives a handover command, such as the processing time delay of an RRC layer, and there is no other limitation on the physical layer; and in the other case, there is downlink data arriving at a network side, if the network considers the terminal not in an uplink-synchronized state, the terminal is triggered by a Physical Downlink Control Channel (PDCCH) signaling to initiate a random access procedure, and there is a time delay requirement on the initiation of a random access after the terminal receives the PDCCH signaling. As the selection on a PRACH resource is determined by a Media Access Control (MAC) layer, a physical random access preamble cannot be sent by a physical layer if the MAC layer does not take the required time delay into consideration when selecting a PRACH resource.